Electrical isolation between two conductive structures, such as metal lines or metal bumps, will not be good in current integrated circuit (IC) without planarization. The electrical isolation problem is caused by re-deposition of conductive material/metal from the wafer holder during pre-sputter cleaning forming stringers between adjacent metal conductive structures causing electrical shorting between the structures.
U.S. Pat. No. 4,704,301 to Bauer et al. describes a metal (e.g. aluminum) coater wafer holder.
U.S. Pat. No. 6,267,852 B1 to Givens et al. describes a wafer holder in a sputter clean tool and method.
U.S. Pat. No. 6,340,405 B1 to Park describes a wafer holder in an etch tool.